1. Field of the Invention
The present invention relates to an image display apparatus responding to diverse video signals having different display conditions.
2. Description of the Related Art
The projector for projecting images is one of the projector-type display apparatuses that display magnified images generated by a computer on a screen. The projector converts analog video signals supplied from an external image supply apparatus into digital video signals, carries out various series of image processing, and generates video signals that can be supplied to a light modulator like an LCD (liquid crystal display). The projector actuates the LCD in response to a generated video signal and modulates light emitted from a light source, thereby displaying a projected image via a projection optical system onto the screen.
The projector is generally required to display images corresponding to video signals having diverse display conditions, for example, video signals generated by the computer corresponding to various formats like VGA, SVGA, and XGA as well as television signals (including high-vision signals) reproduced by video recorders, DVD (digital versatile disc) players, and other reproducing units.
In the process of converting the analog video signal into a digital video signal, quantization noise arises according to the sampling frequency and the frequency component included in the analog video signal. The quantization noise adversely affects the picture quality of the displayed image. It is accordingly preferable to omit the frequency component, which causes the quantization noise, from the analog video signal, prior to conversion of the analog video signal into the digital video signal.
In the structure of displaying images corresponding to diverse display conditions, the wide range of video signals having a relatively low frequency component to a relatively high frequency component are input as the supplied analog video signal. The important issue here is to prevent quantization noise, which may occur in each of the diverse display conditions that lead to input of the wide range of video signals having the relatively low frequency component to the relatively high frequency component.
This issue is not restricted to the projector but arises in any image display apparatus that converts analog video signals into digital video signals and utilizes the converted digital video signals to display images in response to video signals corresponding to diverse display conditions.